U.S. patent application number 14/365467 was filed with the patent office on 2014-10-09 for wind turbine blades.
This patent application is currently assigned to VESTAS WIND SYSTEMS A/S. The applicant listed for this patent is Vestas Wind Systems A/S. Invention is credited to Frank Hoelgaard Hahn, Mark Hancock, Chris Payne.
Application Number | 20140301859 14/365467 |
Document ID | / |
Family ID | 45560559 |
Filed Date | 2014-10-09 |
United States Patent
Application |
20140301859 |
Kind Code |
A1 |
Hancock; Mark ; et
al. |
October 9, 2014 |
WIND TURBINE BLADES
Abstract
A reinforcing structure 9 for a wind turbine blade is in the
form of an elongate stack 27 of layers 31 of pultruded fibrous
composite strips supported within a U-shaped channel 28. The length
of each layer 31 is slightly different to create a taper at the
ends of the stack; the centre of the stack 27 has five layers 31,
and each end has a single layer 31. The ends of each layer 31 are
chamfered, and the stack is coated with a thin flexible pultruded
fibrous composite strip 33 extending the full length of the stack
27. The reinforcing structure 9 extends along a curved path within
the outer shell of the blade. During configuration of the blade
components within a mould 37, the reinforcing structure 9 is
introduced into the mould 37 by sliding the channel 28 along the
surface of an elongate wedge 29 within the mould 37 along the
curved path. The wedge 29 is oriented along its length at an angle
depending on the curvature of the path at that position so as to
guide the reinforcing structure 9 into the desired position. The
regions of the outer shell of the blade on either side of the
reinforcing structure 9 are filled with structural foam 17, and the
reinforcing structure 9 and the foam 17 are both sandwiched between
an inner skin 18 and an outer skin 19.
Inventors: |
Hancock; Mark; (Southampton,
GB) ; Hahn; Frank Hoelgaard; (Ringkobing, DK)
; Payne; Chris; (Bristol, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Vestas Wind Systems A/S |
Aarhus N. |
|
DK |
|
|
Assignee: |
VESTAS WIND SYSTEMS A/S
Aarhus N.
DK
|
Family ID: |
45560559 |
Appl. No.: |
14/365467 |
Filed: |
December 11, 2012 |
PCT Filed: |
December 11, 2012 |
PCT NO: |
PCT/DK2012/050458 |
371 Date: |
June 13, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61588247 |
Jan 19, 2012 |
|
|
|
Current U.S.
Class: |
416/230 ; 156/60;
264/258; 416/229R |
Current CPC
Class: |
Y02E 10/72 20130101;
B29C 70/865 20130101; B29C 70/84 20130101; Y02E 10/721 20130101;
F03D 1/0675 20130101; F05B 2240/301 20130101; Y02P 70/50 20151101;
B29L 2031/085 20130101; F05B 2230/60 20130101; F05B 2230/50
20130101; F05B 2280/6003 20130101; F05B 2280/702 20130101; B29C
70/443 20130101; B29D 99/0025 20130101; Y02P 70/523 20151101; Y10T
156/10 20150115; B29D 99/0028 20130101 |
Class at
Publication: |
416/230 ;
416/229.R; 156/60; 264/258 |
International
Class: |
F03D 1/06 20060101
F03D001/06; B29D 99/00 20060101 B29D099/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2011 |
GB |
1121649.6 |
Claims
1. A wind turbine blade of generally hollow construction and formed
from first and second opposing half-shells; each half-shell
comprising an inner skin and an outer skin and first and second
elongate reinforcing structures being located between the inner and
outer skins; each reinforcing structure extending along the
lengthwise direction of the blade and comprising a stack of layers;
each stack having a thickness which extends in a direction
substantially perpendicular to a surface of the blade; each layer
extending across a width of the respective stack, the width being
perpendicular to the lengthwise direction of the blade and
perpendicular to the thickness of the stack, and each layer
comprising at least one pre-cured pultruded fibrous composite
strip; each half-shell further comprising core material disposed
between the inner and outer skins and extending: (a) between the
first and second elongate reinforcing structures; (b) from the
first elongate reinforcing structure towards a leading edge of the
blade; and (c) from the second elongate reinforcing structure
towards a trailing edge of the blade; the wind turbine blade
further comprising an elongate web extending between at least one
of the reinforcing structures in the first half-shell and at least
one of the reinforcing structures in the second half-shell.
2. The wind turbine blade as claimed in claim 1, wherein the
elongate reinforcing structures and the core material define
abutment edges which are substantially perpendicular to the surface
of the wind turbine blade.
3. The wind turbine blade as claimed in claim 1, further
comprising, within each half-shell, a pre-cured mesh located
between the outer skin and at least one of the elongate reinforcing
structures.
4. The wind turbine blade as claimed in claim 1, further
comprising, within each half-shell, a pre-cured mesh located
between the inner skin and at least one of the elongate reinforcing
structures.
5. The wind turbine blade as claimed in claim 1, further
comprising, within at least one of the half-shells, a pre-cured
mesh located between the outer skin and a region of abutment of one
of the elongate reinforcing structures and the core material.
6. The wind turbine blade as claimed in claim 1, further
comprising, within at least one of the half-shells, a pre-cured
mesh located between the inner skin and a region of abutment of one
of the elongate reinforcing structures and the core material.
7. The wind turbine blade as claimed in claim 3, wherein the or
each pre-cured mesh is formed from glass weave and pre-cured
resin.
8. The wind turbine blade as claimed in claim 1, wherein the layers
are of different lengths such that the thickness of the stack is
tapered towards at least one end.
9. The wind turbine blade as claimed in claim 8, wherein at least
one of the two ends of each layer is chamfered.
10. The wind turbine blade as claimed in claim 1, wherein each
layer comprises a single pultruded fibrous composite strip
extending across the full width of the layer.
11. The wind turbine blade as claimed in claim 1, wherein each
layer comprises a plurality of pultruded fibrous composite
strips.
12. The wind turbine blade as claimed in claim 11, wherein the
plurality of pultruded fibrous composite strips comprises a
parallel configuration of strips within the layers.
13. The wind turbine blade as claimed in claim 12, wherein the
longitudinal edges of the strips within each layer of the stack are
aligned with edges of the strips in the other layers.
14. The wind turbine blade as claimed in claim 12, wherein the
longitudinal inner edges of the strips within each layer of the
stack are staggered with respect to the inner longitudinal edges of
the strips within the or each adjacent layer.
15. The wind turbine blade as claimed in claim 11, wherein the
plurality of pultruded fibrous composite strips comprises a
plurality of strips arranged end to end.
16. The wind turbine blade as claimed in claim 1, wherein the stack
further comprises a covering layer extending the full length of the
stack.
17. The wind turbine blade as claimed in claim 16, wherein the
thickness of the covering layer is substantially less than the
thickness of the other layers within the stack.
18. The wind turbine blade as claimed in claim 1, wherein the
pultruded fibrous composite strips are formed from fibres selected
from: carbon fibres; glass fibres; aramid fibres; and natural
fibres, including wood fibres and organic fibres.
19. The wind turbine blade as claimed in claim 1, further
comprising an elongate support element for supporting the stack of
layers.
20. The wind turbine blade as claimed in claim 19, wherein the
support element comprises a channel of generally U-shaped cross
section, and wherein the stack of layers is supported within the
channel.
21. The wind turbine blade as claimed in claim 19, wherein the
support element is formed from a glass-reinforced plastics (GRP)
material.
22. The wind turbine blade as claimed in claim 1, wherein the web
is formed from a resilient material.
23. The wind turbine blade as claimed in claim 1 and comprising at
least one elongate channel of generally U-shaped cross section in
which an elongate reinforcing structure may be supported.
24. The wind turbine blade as claimed in claim 1, wherein the inner
and outer skins extend substantially uninterrupted across the core
material and the reinforcing structures.
25. A method of manufacturing a wind turbine blade of generally
hollow construction and formed from first and second opposing
half-shells; constructing each half-shell from an inner skin and an
outer skin; locating first and second elongate reinforcing
structures on the outer skin so as to extend along the lengthwise
direction of the blade; each reinforcing structure comprising a
stack of layers, each stack having a thickness which extends in a
direction substantially perpendicular to a surface of the blade;
each layer extending across a width of the respective stack, the
width being perpendicular to the lengthwise direction of the blade
and perpendicular to the thickness of the stack, and each layer
comprising at least one pre-cured pultruded fibrous composite
strip; disposing within each half-shell core material on the outer
skin so as to extend: (a) between the first and second elongate
reinforcing structures; (b) from the first elongate reinforcing
structure towards a leading edge of the blade; and (c) from the
second elongate reinforcing structure towards a trailing edge of
the blade; disposing the inner skin on the upper surface of the
first and second elongate reinforcing structures and the core
material; and disposing an elongate web so as to extend between at
least one of the reinforcing structures in the first half-shell and
at least one of the reinforcing structures in the second
half-shell.
26. A method of manufacturing a wind turbine blade of generally
hollow construction and comprising first and second half-shells;
disposing, in each of a first and second elongated half-mould, one
or more fibre cloths for respective outer skins; locating, in each
of the first and second elongated half-moulds, first and second
elongate reinforcing structures on the fibre cloths for the outer
skins so as to extend along the lengthwise direction of the
respective half-moulds; each reinforcing structure comprising a
stack of layers, each stack having a thickness which extends in a
direction substantially perpendicular to a surface of the
respective half-mould; each layer extending across a width of the
respective stack, the width being perpendicular to the lengthwise
direction of the respective half-mould and perpendicular to the
thickness of the stack, and each layer comprising at least one
pre-cured pultruded fibrous composite strip; disposing within each
of the respective half-mould core material on the fiber cloths for
the outer skin so as to extend: (a) between the first and second
elongate reinforcing structures; (b) from the first elongate
reinforcing structure towards a leading edge of the respective
half-mould; and (c) from the second elongate reinforcing structure
towards a trailing edge of the respective half-mould; disposing, in
each of a first and second elongated half-mould, on upper surfaces
of the first and second elongate reinforcing structures and the
core material, one or more fibre cloths for respective inner skins;
supplying resin into the first and second half-moulds; and
subsequently curing the resin so as to form the first and second
half-shells.
27. The method according to claim 26, comprising subsequently
disposing an elongate web in one of the half-moulds; pivoting the
first half-mould into a position above second half-mould, so as for
the elongate web to extend between at least one of the reinforcing
structures in the first half-shell and at least one of the
reinforcing structures in the second half-shell.
28. The method as claimed in claim 26, further comprising locating,
within at least one of the half-moulds, a pre-cured mesh between
the outer skin and a region of abutment of one of the elongate
reinforcing structures and the core material.
29. The method as claimed in claim 26, further comprising locating,
within at least one of the half-moulds, a pre-cured mesh between
the inner skin and a region of abutment of one of the elongate
reinforcing structures and the core material.
Description
[0001] The present invention relates to rotor blades for wind
turbines and to methods of manufacturing wind turbine blades.
[0002] A typical wind turbine is illustrated in FIG. 1. The wind
turbine 1 comprises a tower 2, a nacelle 3 mounted at top of the
tower 2 and a rotor 4 operatively coupled to a generator 5 within
the nacelle 3. The wind turbine 1 converts kinetic energy of the
wind into electrical energy. In addition to the generator 5, the
nacelle 3 houses the various components required to convert the
wind energy into electrical energy and also the various components
required to operate and optimize the performance of the wind
turbine 1. The tower 2 supports the load presented by the nacelle
3, the rotor 4 and other wind turbine components within the nacelle
3.
[0003] The rotor 4 includes a central hub 6 and three elongate
rotor blades 7a, 7b, 7c of approximately planar configuration which
extend radially outward from the central hub 6. In operation, the
blades 7a, 7b, 7c are configured to interact with the passing air
flow to produce lift that causes the central hub 6 to rotate about
its longitudinal axis. Wind speed in excess of a minimum level will
activate the rotor 4 and allow it to rotate within a plane
substantially perpendicular to the direction of the wind. The
rotation is converted to electric power by the generator 5 and is
usually supplied to the utility grid.
[0004] A conventional rotor blade is made from an outer shell and
an inner hollow elongate spar of generally rectangular cross
section. The spar serves to transfer loads from the rotating blade
to the hub of the wind turbine. Such loads include tensile and
compressive loads directed along the length of the blade arising
from the circular motion of the blade and loads arising from the
wind which are directed along the thickness of the blade, i.e. from
the windward side of the blade to the leeward side.
[0005] An alternative type of rotor blade is known which avoids the
need for an inner spar by incorporating within the outer shell one
or more fibrous reinforcing structures of high tensile strength
which extend along the lengthwise direction of the blade. Examples
of such arrangements are described in EP 1 520 983 and WO
2006/082479. Other arrangements are also described in US
2012/0014804 and WO 2011/088372.
[0006] In these arrangements, use is made of pultruded fibrous
strips of material. Pultrusion is a continuous process similar to
extrusion, wherein fibres are pulled through a supply of liquid
resin and then heated in an open chamber where the resin is cured.
The resulting cured fibrous material is of constant cross section
but, since the process is continuous, the material once formed may
be cut to any arbitrary length. Such a process is particularly
cheap and therefore an attractive option for the manufacture of
reinforcing structures for wind turbine blades.
[0007] The use of cured pultruded strips overcomes problems
associated with conventional arrangements in which non-cured fibres
are introduced into a mould to form parts of a wind turbine blade,
in which there is a risk of the fibres becoming misaligned.
[0008] Furthermore, pultruded strips have the property of absorbing
the very high bending moments which arise during rotation of wind
turbine blades.
[0009] In the above two known arrangements, a relatively large
number of separate elements are used to form the reinforcing
structure, and each element must be individually positioned within
the structure of the shell.
[0010] It would be desirable to provide a suitable reinforcing
structure for a wind turbine blade of this alternative type which
is of simpler construction and therefore cheaper to
manufacture.
[0011] US 2009/0269392 describes a wind turbine blade comprising
elongate structural members formed from laminated fibre cloths
infiltrated with resin.
[0012] However, in this arrangement the fibre cloths are cured in
situ which requires the cloths to be carefully positioned and
correctly oriented on the surface of the shell prior to
moulding.
[0013] It would therefore be desirable to provide a wind turbine
blade which overcomes, or at least mitigates, some or all of the
above disadvantages of known wind turbine blades.
[0014] Thus, in accordance with a first aspect of the present
invention there is provided a wind turbine blade of generally
hollow construction and formed from first and second opposing
half-shells; each half-shell comprising an inner skin and an outer
skin and first and second elongate reinforcing structures being
located between the inner and outer skins; each reinforcing
structure extending along the lengthwise direction of the blade and
comprising a stack of layers; each stack having a thickness which
extends in a direction substantially perpendicular to a surface of
the blade; each layer extending across a width of the respective
stack, the width being perpendicular to the lengthwise direction of
the blade and perpendicular to the thickness of the stack, and each
layer comprising at least one pre-cured pultruded fibrous composite
strip; each half-shell further comprising core material disposed
between the inner and outer skins and extending: (a) between the
first and second elongate reinforcing structures; (b) from the
first elongate reinforcing structure towards a leading edge of the
blade; and (c) from the second elongate reinforcing structure
towards a trailing edge of the blade; the wind turbine blade
further comprising an elongate web extending between at least one
of the reinforcing structures in the first half-shell and at least
one of the reinforcing structures in the second half-shell.
[0015] The stack functions within the wind turbine blade as a spar
cap. Preferably, the width of each stack extends within the blade,
in use, in a generally chordwise direction within a plane
substantially parallel to the surface of the blade. Preferably, in
a cross-section oriented transversely to the lengthwise direction
of the blade, each stack has the shape of an oblong rectangle,
wherein the thickness of the stack is parallel to the shorter sides
of the rectangle and the width of the rectangle is parallel to the
longer sides of the rectangle.
[0016] The web is elongate in the lengthwise direction of the
blade. It extends in a transverse direction between at least one of
the reinforcing structures in the first half-shell and at least one
of the reinforcing structures in the second half-shell. As
exemplified below, the blade can have two I-shaped or C-shaped
webs, each extending between one of the reinforcing structures in
the first half-shell and one of the reinforcing structures in the
second half-shell. In other embodiments, some of which are
described below, the blade has a web with an X-shaped
cross-section, extending between two reinforcing structures in the
first half-shell and two reinforcing structures in the second
half-shell.
[0017] A major technical advantage of providing at least two such
reinforcing structures within each half-shell arises from the
curvature of the wind turbine blade. In order to achieve the
desired curvature, the inner surfaces of the moulds used to
manufacture the half-shells are also curved, and this imparts a
corresponding curvature to the inner and outer skins during the
moulding process. Since the upper and lower surfaces of the stacks
are substantially planar, this gives rise to a gap between the
surfaces of the stacks and the curved inner and outer skins, which
will be filled with resin during moulding. In order to optimise the
strength of the resulting turbine blade, it is desirable to reduce
the size of the gap. Wth the present invention, this is achieved by
providing at least two reinforcing structures within each
half-shell, such that each structure can have a smaller width than
would be required when only a single reinforcing structure is
provided.
[0018] The elongate reinforcing structures and the core material
define abutment edges which are preferably substantially
perpendicular to the surface of the wind turbine blade. Such an
arrangement is advantageous in that it permits the reinforcing
structures to be manufactured a low cost. Furthermore, during the
moulding operation, it is possible to place the core material in
the mould before the reinforcing structures, and to use the edges
of the core material to assist in the location of the reinforcing
structures in the mould. This would not necessarily always be
possible if the abutment edges of the reinforcing structures were
not perpendicular. The perpendicular direction is also the
thickness direction of the wind turbine blade.
[0019] The wind turbine blade preferably further comprises, within
each half-shell, a pre-cured mesh located between the outer skin
and at least one of the elongate reinforcing structures. In
addition or alternatively, the wind turbine blade preferably
further comprises, within each half-shell, a pre-cured mesh located
between the inner skin and at least one of the elongate reinforcing
structures. In each case, the mesh may be made from glass weave and
pre-cured resin. The blade preferably comprises, within at least
one of the half-shells, a pre-cured mesh located between the outer
skin and a region of abutment of one of the elongate reinforcing
structures and the core material. The blade preferably comprises,
within at least one of the half-shells, a pre-cured mesh located
between the inner skin and a region of abutment of one of the
elongate reinforcing structures and the core material.
[0020] Such meshes provide additional stiffness at the transition
regions between the reinforcing structures and the core material.
In addition, the meshes effectively prevent wrinkling of the inner
and outer skins of the turbine blades which could otherwise occur
when there are gaps between the underlying reinforcing structures
and the core material or when the thickness of the reinforcing
structures is different from the thickness of the core
material.
[0021] The stack preferably has a substantially rectangular cross
section throughout its length and/or preferably a substantially
constant width. Furthermore, the pultruded fibrous composite strips
are preferably of substantially uniform cross section.
[0022] By forming the reinforcing structure from a stack of layers,
it is possible to form the entire reinforcing structure as a
separate component and then to incorporate the entire reinforcing
structure in a single operation.
[0023] Furthermore, since pultruded fibrous composite strips are
cheap to manufacture, and can readily be cut to any desired length,
the resulting reinforcing structure can therefore be conveniently
constructed at low cost.
[0024] An additional advantage of this arrangement is that it
becomes possible to adjust the thickness of the stack at any point
along its length, so as to conform to the desired thickness profile
of the outer shell of the wind turbine blade, simply by selecting
the number of layers to be incorporated in the stack at that point.
It is therefore possible to form the reinforcing structure with any
desired thickness profile, which matches the tapering shape of the
turbine blade.
[0025] It is normally desirable in wind turbine blades to provide a
greater degree of reinforcement along the central section of the
blade along the longitudinal axis of the blade, i.e. the region
mid-way between the root and the tip of the blade, since this is
where most of the tensile stresses are encountered by the blade.
Thus, a particularly desirable thickness profile is one where the
central section of the reinforcing structure is of maximum
thickness, and where one or both of the end sections are of minimum
thickness.
[0026] It is therefore preferred that the layers within the
reinforcing structure are of different lengths such that the
thickness of the stack is tapered towards at least one end.
[0027] In the simplest arrangement, in which each layer of the
stack has ends which are square-cut, this will result in a stack
having a stepwise taper, the height of each step being the
thickness of each layer. To reduce the concentration of stresses at
the ends of the layers, it would be desirable for the thickness
profile at the end of the stack to be smoother. It is therefore
preferred that at least one of the two ends of each layer be
chamfered. In this way, the upper surface of the stack can be made
smoother along its full length.
[0028] Even still, unless the chamfer is of a sufficiently small
angle, there will still be discontinuities in the gradient along
the tapered ends.
[0029] To increase the smoothness even further, it is preferred
that the stack further comprise a covering layer extending the full
length of the stack. Such a covering layer may be have a thickness
which is substantially less than the thickness of the other layers
within the stack, for example the covering layer may be one quarter
of the thickness of the other layers. This enables the covering
layer to be sufficiently flexible so as to "bed down" on the upper
surface of the stack and thereby smoothen out the changes in the
orientation of the underlying surface.
[0030] For example, in the preferred embodiment, there are five
layers within each stack, and the thickness of each layer is
approximately 4 mm, i.e. between 3.5 mm and 4.5 mm, whereas the
thickness of the covering layer is only approximately 1 mm, i.e.
between 0.5 mm and 1.5 mm. The advantage of a thickness of 4 mm for
each layer is that the pultruded strips can be supplied in a
roll.
[0031] The width of each layer is preferably about 150 mm, i.e.
between 140 mm and 160 mm, since this provides the necessary degree
of edgewise stiffness to prevent substantial edgewise
vibration.
[0032] Other embodiments are envisaged in which there may be as few
as 4 layers or as many as 12 layers within each stack.
[0033] Each layer within the stack, other than the covering layer,
when provided, may comprise a single pultruded fibrous composite
strip extending across the full width of the layer. Such an
arrangement has the advantage of simplicity and hence low
manufacturing cost, since only one strip is required within each
layer. Furthermore, since each layer within the stack has the same
width, all of the pultruded fibrous composite strips, other than
the covering layer when provided, can be made from the same
pultrusion apparatus, or indeed may be cut from the same pultruded
strip.
[0034] Alternatively, each layer may comprise a parallel
arrangement of a plurality of pultruded fibrous composite strips.
This may take the form of a first configuration in which the side,
or longitudinal, edges of the strips within each layer of the stack
the inn are aligned with side (longitudinal) edges of the strips in
the other layers, in which case each strip will be of a smaller
width than with the above arrangement in which each layer comprises
only one strip. However, the strips can still have the same width
and therefore be formed from the same pultrusion apparatus or cut
from the same pultruded strip. In a second configuration, the inner
side (longitudinal) edges of the strips within each layer of the
stack are staggered with respect to the inner side edges of the
strips within the or each adjacent layer. Although this means that
not all of the strips will have the same width and must therefore
be formed from more than one pultrusion apparatus, this can result
in a more stable stack. Indeed, such a configuration is typically
found in a brick wall.
[0035] In each of the above arrangements in which each layer
comprises more than one strip, the strips within each layer may
alternatively, or in addition, be arranged end to end. This could
be advantageous, for example, where the reinforcing structure is of
a substantially length, in which case the manufacture could be
simplified by forming the reinforcing structure from a number of
relatively short pultruded strips.
[0036] It is important that the pultruded fibrous composite strips
are of sufficient tensile strength, but can be formed from fibres
selected from: carbon fibres; glass fibres; aramid fibres; and
natural fibres, including wood fibres and organic fibres, including
combinations of any of these types of fibre. In the preferred
embodiment the pultruded fibrous composite strips are formed from
carbon fibres embedded in a thermoset resin matrix. Carbon fibres
are particularly desirable due to their high strength-to-weight
ratio in comparison to other fibres such as glass fibres.
[0037] In a preferred embodiment, the reinforcing structure
includes an elongate support element for supporting the stack of
layers. This assists in the process of moving the entire
reinforcing structure, when formed, into the desired position
within the wind turbine blade. The preferred configuration of the
support element is a channel having a generally U-shaped cross
section, and wherein the stack of layers is supported within the
channel. This is particularly convenient since the stack is
substantially rectangular in cross section. It is especially
preferred that at least the width of the U-shaped cross section
correspond to the width of the stack, since in this case the side
arms of the U-shape will prevent any undesirable lateral movement
of the layers within the stack during transportation.
[0038] The support element may conveniently be made from a
glass-reinforced plastics (GRP) material and may also either
comprise or contain a lightning conductor.
[0039] As above, the support element is preferably formed from a
glass-reinforced plastics (GRP) material and may comprise a
lightning conductor.
[0040] The skins are preferably made from GRP.
[0041] With this arrangement, each half-shell can be formed
separately and then the two halves joined together before the
entire shell, with the reinforcing structures in position, is cured
by heating.
[0042] The inner and outer skins of the half-shells may be made
from a glass fibre epoxy resin composite.
[0043] The wind turbine blade preferably further comprises at least
one elongate web located between the reinforcing structures within
the opposing half-shells so as to transfer shear forces acting on
the wind turbine blade in use. Such as web may therefore be
referred to as a "shear web". The combination of two such
reinforcing structures and the web emulates, and possesses the
structural advantages of, an I-beam.
[0044] In one embodiment, each shell comprises two reinforcing
structures, and the elongate web is X-shaped in cross section. In
this case, each of the two diagonals of the X-shape preferably
extends between a respective two of the reinforcing structures.
Such an arrangement enables a single web to be provided for four
reinforcing structures.
[0045] The X-shaped web is preferably formed from two V-shaped webs
connected together, since V-shaped webs can readily be stacked or
nested for ease of storage and transport.
[0046] Furthermore, the web is preferably made from a resilient
material so as to conform more readily to the shape of the mould
during manufacture of the turbine blades.
[0047] The X-shaped resilient web is preferably made slightly
larger than the distance between the two half-shells, so that the
web will flex to some extent when the half-shells are brought
together. Not only does allow for greater tolerances in the size of
the web, but also enables a good adhesive bond to be established
between the web and the half-shells. Once the adhesive is cured,
the web is locked in the desired position, and the height of the
web matches the separation between the two half-shells.
[0048] In this case, the web preferably comprises a respective
flange at each end of the two diagonals of the X-shaped cross
section, so as to direct the shear force from the full width of
each reinforcing structure into the web.
[0049] As an alternative to the provision of an X-shaped web, a
conventional C-shaped web may be provided, where the two arms of
the C-shape may constitute flanges for attaching the web between
the outer half-shells of the blade.
[0050] An additional web having a Z-shaped cross section may also
be provided. This is particularly desirable when there are six
reinforcing structures, since an X-shaped web may be provided for
absorption of the shear forces between four opposing reinforcing
structures, typically within the leading edge of the blade, and the
Z-shaped web may then be provided for absorbing the shear forces
between the remaining two opposed reinforcing structures, typically
within the trailing edge portion of the blade, i.e. positioned
between the X-shaped web and the trailing edge of the blade. The
terms "leading edge" and "trailing edge" will be described in
greater detail below.
[0051] In a preferred arrangement, four of the reinforcing
structures extend in generally parallel directions along the length
of the blade, whereas the remaining two reinforcing structures are
shorter and extend away from the other reinforcing structures at
the wider sections of the blade to form "rear stringers". The
resulting separation of the reinforcing structures at the wide
portions of the blade gives rise to improved edgewise stiffness.
The provision of the rear stringers also reduces the length of the
unsupported blade shell between the main structure and the trailing
edge, which, in turn, enables the structural foam in the blade to
be thinner. By retaining separation between the reinforcing
structures at the root end of the blade, the termination of the
structures can be effected with a reduced concentration of
stresses.
[0052] The upper and lower arms of the Z-shape preferably serve as
flanges for connecting the web between the two outer half-shells of
the blade, e.g. by applying a layer of adhesive to the exposed
outer surfaces of the arms. Thus, only the central section of the
Z-shaped web extends into the space between the associated
reinforcing structures.
[0053] In the case of a X-shaped web, the diagonals of the X-shape
are preferably bent at the intersection, such that the angle
between two adjacent arms is different from the angle between the
other two arms.
[0054] Alternatively, the web may be of a Y-shaped cross
section.
[0055] In each case, the web or webs are preferably formed from a
resilient material. This is of particular benefit when upper and
lower half-shells are connected together with the webs in position
between the half-shells but physically attached to only the lower
half-shell, since, on joining the two half-shells together, the
free ends of the webs to which a layer of adhesive may be applied
will exert a force against the upper half-shell which is sufficient
to cause the free ends of the webs to adhere to the upper
half-shell.
[0056] In all of the above-described arrangements, the inner and
outer skins preferably extend substantially uninterrupted across
the core material and the reinforcing structures.
[0057] In accordance with a further aspect of the present
invention, there is provided a method of manufacturing a wind
turbine blade of generally hollow construction and formed from
first and second opposing half-shells; constructing each half-shell
from an inner skin and an outer skin; locating first and second
elongate reinforcing structures on the outer skin so as to extend
along the lengthwise direction of the blade; each reinforcing
structure comprising a stack of layers, each stack having a
thickness which extends in a direction substantially perpendicular
to a surface of the blade; each layer extending across a width of
the respective stack, the width being perpendicular to the
lengthwise direction of the blade and perpendicular to the
thickness of the stack, and each layer comprising at least one
pre-cured pultruded fibrous composite strip; disposing within each
half-shell core material on the outer skin so as to extend: (a)
between the first and second elongate reinforcing structures; (b)
from the first elongate reinforcing structure towards a leading
edge of the blade; and (c) from the second elongate reinforcing
structure towards a trailing edge of the blade; disposing the inner
skin on the upper surface of the first and second elongate
reinforcing structures and the core material; and disposing an
elongate web so as to extend between at least one of the
reinforcing structures in the first half-shell and one of the
reinforcing structures in the second half-shell.
[0058] In a preferred embodiment, the method comprises
manufacturing a wind turbine blade of the above type, in which the
one or more reinforcing structures extend at least part way along
the length of the wind turbine blade along a respective
predetermined curve defined by the outer profile of the wind
turbine blade, the method comprising, for the or each reinforcing
structure: providing a substantially rigid elongate support surface
within a mould, the support surface extending along the
predetermined curve and which is oriented at each position along
the predetermined curve at an angle which depends on the degree of
curvature at that position, thereby to facilitate accurate
positioning of the reinforcing structure; introducing the support
element into the mould; and positioning the reinforcing structure
along the support surface.
[0059] The step of positioning the reinforcing structure may be
achieved by sliding the support element along the support surface
towards the predetermined curve.
[0060] By suitably orienting the support surface in this way,
analogous to the banking of roads at bends, the support element can
be moved into the desired final position within the mould by
sliding it along the support surface. In this way, the support
surface thus acts as a steering or guiding surface for the
reinforcing structure.
[0061] It is preferred that the stack is placed on the support
element as a first step, and that the complete reinforcing
structure is moved into position in this way, although it would of
course be possible to move only the support element into its
desired position within the mould as a first step, and then to
introduce the stack into the mould, e.g. by sliding the stack along
the support element. It would alternatively be possible to
introduce the individual layers of the stack into the mould one at
a time.
[0062] The support surface may conveniently be one surface of an
elongate wedge arranged on the surface of the mould. In this case,
the wedge may be made from structural foam.
[0063] In a preferred embodiment, the wind turbine blade comprises
at least one elongate reinforcing structure which extends in the
lengthwise direction of the wind turbine blade along a respective
predetermined curve defined by the outer profile of the wind
turbine blade, and each reinforcing structure comprises a
reinforcing element supported within a channel of generally
U-shaped cross section, and the method comprises positioning each
reinforcing structure within a mould.
[0064] In this case, the channel may first be positioned within the
mould, and then the reinforcing element placed into the channel.
Alternatively, the reinforcing element may first be positioned
within the channel, and then the entire reinforcing structure, i.e.
the channel containing the reinforcing element, may then be
positioned within the mould.
[0065] A substantially rigid elongate support surface may
advantageously be provided within the mould, the support surface
extending along the predetermined curve and which is oriented at
each position along the predetermined curve at an angle which
depends on the degree of curvature at that position, thereby to
facilitate accurate positioning of the reinforcing structure; and
the method preferably comprises: introducing the reinforcing
structure into the mould; and positioning the reinforcing structure
along the support surface, e.g. by sliding the support element
along the support surface towards the predetermined curve.
[0066] The steps of introducing the pre-cured stack and the other
structural elements can be performed in any desired sequence.
[0067] Alternatively, the or each reinforcing structure may be
built up from the U-shaped channel and the individual pultruded
strips in situ within the mould.
[0068] Although in the preferred embodiment, there are six
reinforcing structures within the turbine blade, there may of
course be either fewer or more, depending on the size and/or shape
of the turbine blade and the degree of reinforcement required.
[0069] The invention also provides a method of manufacturing a wind
turbine blade of generally hollow construction and comprising first
and second half-shells; [0070] disposing, in each of a first and
second elongated half-mould, one or more fibre cloths for
respective outer skins; [0071] locating, in each of the first and
second elongated half-moulds, first and second elongate reinforcing
structures on the fibre cloths for the outer skins so as to extend
along the lengthwise direction of the respective half-moulds;
[0072] each reinforcing structure comprising a stack of layers,
each stack having a thickness which extends in a direction
substantially perpendicular to a surface of the respective
half-mould; [0073] each layer extending across a width of the
respective stack, the width being perpendicular to the lengthwise
direction of the respective half-mould and perpendicular to the
thickness of the stack, and each layer comprising at least one
pre-cured pultruded fibrous composite strip; [0074] disposing
within each of the respective half-mould core material on the fiber
cloths for the outer skin so as to extend: (a) between the first
and second elongate reinforcing structures; (b) from the first
elongate reinforcing structure towards a leading edge of the
respective half-mould; and (c) from the second elongate reinforcing
structure towards a trailing edge of the respective half-mould;
[0075] disposing, in each of a first and second elongated
half-mould, on upper surfaces of the first and second elongate
reinforcing structures and the core material, one or more fibre
cloths for respective inner skins; [0076] supplying resin into the
first and second half-moulds; and [0077] subsequently curing the
resin so as to form the first and second half-shells.
[0078] Preferably, the method comprises subsequently disposing an
elongate web in one of the half-moulds; pivoting the first
half-mould into a position above second half-mould, so as for the
elongate web to extend between at least one of the reinforcing
structures in the first half-shell and at least one of the
reinforcing structures in the second half-shell. Preferably, the
method comprises locating, within at least one of the half-moulds,
a pre-cured mesh between the outer skin and a region of abutment of
one of the elongate reinforcing structures and the core material.
Preferably, the method comprises locating, within at least one of
the half-moulds, a pre-cured mesh located between the inner skin
and a region of abutment of one of the elongate reinforcing
structures and the core material.
[0079] Further aspects of the present invention are as follows:
[0080] (a) An elongate reinforcing structure for a wind turbine
blade, the structure being arranged to extend, in use, along the
lengthwise direction of the blade, the structure comprising a stack
of layers, the stack having a width which extends, in use, in a
direction generally parallel to a surface of the wind turbine
blade, each layer extending across the width of the stack and
comprising at least one pultruded fibrous composite strip.
[0081] Such a reinforcing structure is of simpler construction than
known structures and is therefore cheaper to manufacture.
[0082] It will be appreciated that the support element for the
reinforcing structure which is described above in relation to a
preferred embodiment provides advantages which are not necessarily
limited to the particular type of reinforcing structure.
Consequently, the present invention extends to:
[0083] (b) A wind turbine blade comprising at least one elongate
channel of generally U-shaped cross section in which an elongate
reinforcing structure may be supported.
[0084] It will be appreciated that the provision of a web having an
X-shaped cross section provides advantages to wind turbine blades
having reinforcing structures which are not necessarily of the
types described above. For this reason, the present invention
extends to:
[0085] (c) A wind turbine blade of generally hollow construction,
the blade being formed from two opposing half-shells, each
half-shell comprising at least two elongate reinforcing structures
each extending along the lengthwise direction of the blade, and
further comprising a web located between the reinforcing structures
within the opposing half-shells so as to transfer shear forces
acting on the wind turbine blade in use, the web having an X-shaped
cross section.
[0086] (d) A wind turbine blade of generally hollow construction,
the blade being formed from first and second opposing half-shells,
the first half-shell comprising at least two elongate reinforcing
structures and the second half-shell comprising at least one
elongate reinforcing structure, each extending along the lengthwise
direction of the blade, and further comprising a web located
between the reinforcing structures within the opposing half-shells,
the web having a Y-shaped cross section.
[0087] (e) A method of manufacturing a wind turbine blade of the
above type, in which the one or more reinforcing structures extend
at least part way along the length of the wind turbine blade along
a respective predetermined curve defined by the outer profile of
the wind turbine blade, the method comprising, for the or each
reinforcing structure: providing a substantially rigid elongate
support surface within a mould, the support surface extending along
the predetermined curve and which is oriented at each position
along the predetermined curve at an angle which depends on the
degree of curvature at that position, thereby to facilitate
accurate positioning of the reinforcing structure; introducing the
support element into the mould; and positioning the reinforcing
structure along the support surface.
[0088] (f) A method of manufacturing a wind turbine blade
comprising at least one elongate reinforcing structure which
extends in the lengthwise direction of the wind turbine blade along
a respective predetermined curve defined by the outer profile of
the wind turbine blade, and wherein the or each reinforcing
structure comprises a reinforcing element supported within a
channel of generally U-shaped cross section, the method comprising,
for the or each reinforcing structure, positioning the reinforcing
structure within a mould.
[0089] (g) A method of manufacturing a wind turbine blade
comprising at least one elongate reinforcing structure which
extends in the lengthwise direction of the wind turbine blade along
a respective predetermined curve defined by the outer profile of
the wind turbine blade, the method comprising, for the or each
reinforcing structure: providing a substantially rigid elongate
support surface within the mould, the support surface extending
along the predetermined curve and which is oriented at each
position along the predetermined curve at an angle relative to the
surface of the mould which depends on the degree of curvature at
that position, thereby to facilitate accurate positioning of the
reinforcing structure; introducing the reinforcing structure into
the mould; and positioning the reinforcing structure along the
support surface, e.g. by sliding the support element along the
support surface towards the predetermined curve.
[0090] The or each reinforcing structure may be formed and
pre-cured in a separate mould and then introduced, together with
the other components of the wind turbine blade, into the main
mould. With such an arrangement, it is possible to introduce the
pre-cured reinforcing structure into the main mould without the use
of the U-shaped channels or wedge-shaped supports described
above.
[0091] Furthermore, such a procedure is advantageous with
reinforcing structures other than those described above. For
example, reinforcing structures made from fibre cloths, as opposed
to pultruded strips, could be pre-cured in this way and then
introduced into the main mould for forming a wind turbine blade. In
this case, each fibre cloth could be introduced separately into the
mould, or a complete stack of fibre cloths formed as a first step,
which is then placed into the mould.
[0092] Thus, in accordance with a further aspect of the present
invention, there is provided:
[0093] (h) A method of manufacturing a wind turbine blade
comprising at least one reinforcing structure, the method
comprising: forming a stack of fibrous layers; pre-curing the stack
of fibrous layers in a first mould; introducing the pre-cured stack
into a second mould; introducing other structural elements of the
wind turbine into the second mould; and integrating the stack and
the other structural elements together in the second mould.
[0094] In order that the present invention may more readily be
understood, preferred embodiments thereof will now be described
with reference to the accompanying drawings, in which:
[0095] FIG. 1 illustrates the main structural components of a wind
turbine;
[0096] FIG. 2 is a schematic illustration of the inner surface of
one half of the outer shell of a wind turbine blade incorporating
reinforcing structures in accordance with a preferred embodiment of
the present invention;
[0097] FIGS. 3(a) and 3(b) are cross-sectional sketches of
arrangements of reinforcing structures within a half-shell of a
wind turbine blade;
[0098] FIGS. 4(a) to 4(e) are schematic longitudinal
cross-sectional views of a wind turbine blade incorporating the
reinforcing structures shown in FIG. 2;
[0099] FIG. 5 illustrates a lateral cross-sectional view of part of
one of the reinforcing structures illustrated in FIG. 2;
[0100] FIGS. 6(a) to 6(c) illustrate longitudinal sections of three
different embodiments of reinforcing structures in accordance with
the present invention;
[0101] FIGS. 7(a) and 7(b) are two schematic representations of an
X-section web, in accordance with a preferred embodiment, at
different positions along the length of a wind turbine blade;
[0102] FIG. 8 is a longitudinal cross-sectional view of a
reinforcing structure mounted within a mould during the manufacture
of a wind turbine blade in accordance with a preferred
embodiment;
[0103] FIGS. 9(a) and 9(b) illustrate a method of manufacturing a
wind turbine blade in accordance with a preferred embodiment of the
present invention;
[0104] FIGS. 10(a) to 10(f) illustrate alternative forms of web, in
accordance with further embodiments, shown at different positions
along the length of a wind turbine blade;
[0105] FIGS. 11(a) and 11(b) illustrate further alternative forms
of web, in accordance with embodiments of the present
invention;
[0106] FIG. 12 is a flowchart illustrating steps in the manufacture
of a wind turbine blade in accordance with a preferred embodiment
of the present invention;
[0107] FIG. 13 illustrates an alternative method in the manufacture
of a wind turbine in accordance with an embodiment of the present
invention;
[0108] FIG. 14 is a flowchart illustrating the steps in the method
shown in FIG. 12; and
[0109] FIGS. 15(a) to 15(c) illustrate a preferred embodiment in
which meshes are provided in each half-shell of the wind turbine
blade.
[0110] Throughout the following description of the preferred
embodiments of the present invention, and in the drawings, the same
reference numerals are used to indicate the same, or corresponding,
structural features.
[0111] Referring to FIG. 2, one half 8 of the outer shell of a wind
turbine blade is formed with three elongate reinforcing structures
9, 10, 11, to be described in greater detail below.
[0112] Two of the reinforcing structures 9, 10 extend substantially
along the full length of the turbine blade from the root section 12
to the blade tip 13. The root section 12 of the blade is formed
with threaded metallic inserts 14 for receiving bolts by which the
blade is attached to the central hub of the wind turbine, as
described above with reference to FIG. 1.
[0113] The third reinforcing structure 11 extends only part-way
along the blade from the root section 12 and is also laterally
displaced from the other two reinforcing structures 9, 10 towards
the trailing edge 15 of the blade and away from the leading edge 16
of the blade.
[0114] The two reinforcing structures 9, 10 form the spar caps of
the wind turbine blade and the third reinforcing structure 11 acts
as a stiffener for the trailing edge 15.
[0115] The ends of the three reinforcing structures 9, 10, 11
within the root section 12 of the blade are encased in a
glass-reinforced plastics (GRP) material for added strength and
stability, as are the distal ends of the two reinforcing structures
9, 10 which extend to the blade tip 13.
[0116] The remaining portions of the outer shell are filled with
structural foam 17, and the reinforcing structures 9, 10, 11 and
the structural foam 17 are all formed within an outer skin and an
inner skin to be described in greater detail below.
[0117] The structural foam 17 is a lightweight core material, and
it will be appreciated that other core materials can be used, such
as wood, particularly balsa wood, and honeycomb.
[0118] The complete turbine blade is formed from the upper half 8
of the outer shell shown in FIG. 2, together with a corresponding
lower half and two internal webs.
[0119] FIG. 3(a) illustrates a cross-sectional view of a
conventional arrangement in which each half-shell 8' comprises an
inner skin 18' and an outer skin 19' between which only a single
reinforcing structure 9' is provided. The regions between the inner
skin 18' and the outer skin 19' to each side of the reinforcing
structure 9' are filled with structural foam 17'. As can be seen
from the drawing, there is a significant curvature across the width
of the half-shell 8'. Since the reinforcing structure 9' is formed
with a substantially rectangular cross-section, it follows that
that substantial voids 20' are formed between the outer skin 19'
and the central region of the reinforcing structure 9', and between
the inner skin 18' and the end regions of the reinforcing structure
9'. During the moulding stage, to be described in detail below,
resin is introduced into these voids 20', which is undesirable in a
composite structure, since this increases both the weight and the
cost of the blade, and could also give rise to structural
problems.
[0120] FIG. 3(b) is a cross-sectional view of a preferred
embodiment of the present invention in which each half-shell 8 is
provided with at least two reinforcing structures 9, 10 provided
between the inner skin 18 and the outer skin 19. As can be seen,
the volume of the resulting voids 20 which are formed between the
outer skin 19 and the central region of the reinforcing structure
9, and between the inner skin 18 and the end regions of the
reinforcing structure 9 is substantially less than that of the
voids 20' which occur when only a single reinforcing structure 9'
is provided. As a result, the amount of resin required to fill the
voids 20 during the moulding process is substantially less.
[0121] In addition, by using two reinforcing structures in each
half shell, as shown FIG. 3(b), as opposed to the single
reinforcing structure shown in FIG. 3(a), the overall widths of the
reinforcing structures are located more closely to the outer skin
19 of the wind turbine blade. This is advantageous for structural
reasons, since it provides a higher second moment of inertia such
that the wind turbine blade has a greater resistance to
bending.
[0122] FIGS. 4(a) to 4(e) are cross-sectional representations of
the complete turbine blade at different positions along the length
of the blade. FIG. 4(a) represents the blade near the blade tip 13,
from which it can be seen that only the first two reinforcing
structures 9, are present at this position along length of the
upper half of the outer shell shown in FIG. 2. The lower half 21 of
the outer shell is also provided with three reinforcing structures
22, 23, 24, again only two of which 22, 23 are present at this
position.
[0123] A resilient elongate web 25 made from a layer of balsa wood
or lightweight foam sandwiched between two outer layers of GRP and
having a generally X-shaped longitudinal cross section is provided
within the outer shall and serves to transfer the shear forces
which act on the turbine blade in use. One of the two diagonal arms
of the X-shape extends between a first pair of the reinforcing
structures 9, 23, and the other diagonal arm extends between a
second pair of the reinforcing structures 10, 22.
[0124] In FIG. 4(b), which represents a position along the length
of the turbine blade between that of FIG. 4(a) and the central
section, the end-portions of the two remaining reinforcing
structures 11, 24 can be seen.
[0125] FIG. 4(c) represents the central section of the turbine
blade, from which it can be seen that a further resilient elongate
web 26 having a generally Z-shaped longitudinal cross section is
provided which extends between the two reinforcing structures 11,
24 at the trailing edge 15 of the blade. The two outer limbs of the
Z-shape act as flanges for connecting the Z-shaped web 26 to the
two associated reinforcing structures 11, 24.
[0126] Referring to FIG. 4(d), which is a detail of the
cross-sectional view of FIG. 4(c), the reinforcing structure 22 is
sandwiched between the inner skin 18 and the outer skin 19, and the
remaining parts of the outer shell are formed from a layer of
structural foam 17, also sandwiched between the inner and outer
skins 18, 19. The skins are made from GRP.
[0127] The reinforcing structure 22 is in the form of a stack 27 of
layers of pultruded fibrous composite strips supported within a
U-shaped channel 28, which in turn is supported on an elongate
wedge 29 such that the base of the channel 28 is at an acute angle
to the outer skin 19 of the shell. The channel 28 includes material
which acts as a lightning conductor in use. In other embodiments,
the U-shaped channel 28 and the wedge 29 may be omitted.
[0128] The end of the arm of the X-shaped web 25 is provided with a
flange 30 for directing the shear force applied across the full
width of the reinforcing structure 22 to the X-shaped web 25.
[0129] It will be appreciated that the enlarged view shown in FIG.
4(d) applies equally to each of the six reinforcing structures 9,
10, 11, 22, 23, 24.
[0130] FIG. 4(e) illustrates a cross-sectional view of the blade
between the central section represented in FIG. 4(c) and the root
section 12, and it can be seen that the reinforcing structures 9,
10, 11, 22, 23, 24 within each half-shell are closer together than
at the central section of the blade, reflecting the curvature of
the reinforcing structures.
[0131] In FIGS. 4(a) to 4(e) it can be seen that the reinforcing
structures 9, 10, 22 and 23 are spar caps which, together with the
shear webs 25, form the main structural spar of the wind turbine
blade. The reinforcing structures 11 and 24 at the trailing edge
stiffen the wind turbine blade in the region of the trailing edge
to provide stability against buckling and, together with the web
26, form a trailing edge spar.
[0132] Each of the stacks 27 of the reinforcing structures 9, 10,
11, 22, 23, 24 is tapered longitudinally at both ends. This is
achieved by a reduction in the number of layers of pultruded
fibrous strips from five at the central section to only a single
layer at each end. This feature is indicated in the drawings,
wherein, in FIGS. 4(a) and 4(e), the respective stacks 27 of the
reinforcing structures 9, 10, 22, 23, 24 have only a single layer,
whereas the stacks 27 within the central section illustrated in
FIG. 4(c) have five layers. Equally, in FIG. 4(b), the stacks 27 of
the reinforcing structures 9, 10, 22, 23 at the ends of the
X-shaped web 25 have five layers, whereas the stacks 27 of the
reinforcing structures 11, 24 at the ends of the Z-shaped web 26
have only a single layer.
[0133] This feature enables the reinforcing structures 9, 10, 11,
22, 23, 24 to adopt a profile consistent with the thickness profile
of the outer shell of the blade.
[0134] This is further illustrated in the side cross-sectional view
of FIG. 5, which shows how the thickness of the stack 27 of five
layers 31 is tapered towards both the root end 12 and the distal
end 32. It should be emphasised that the drawing is merely
illustrative of the tapered arrangement: in practice, the tapering
may be distributed throughout a large part of the length of the
reinforcing structure.
[0135] Two further features of the preferred embodiment enhance the
smoothness of the tapering so as reduce the impact of stresses
which would arise with discontinuities in the surface profile of
the stack 27. First, each layer 31 is chamfered at both ends so as
to remove the square-cut ends which are formed during the cutting
of the pultruded strips which form the layers 31. Secondly, the
stack 27 is covered with a top layer 33 formed from an additional
pultruded fibrous composite strip having a lesser thickness than
that of the underlying layers 31. Since the top layer 33 is thinner
than the other layers 31, it is also more flexible and therefore
able to bend around the angled chamfered ends of the stack 27
within the tapered end regions to form a relatively smooth upper
surface.
[0136] Each layer 31 within the stack has a thickness of
approximately 4 mm, and the thickness of the top layer is
approximately 1 mm.
[0137] FIGS. 6(a) to 6(c) are longitudinal cross-sectional views
showing three different arrangements of pultruded fibrous composite
strips, or pultrusion strips 34 within the five layers 31. In FIG.
6(a), each layer 31 has only a single pultrusion strip 34 within
each layer. In FIG. 6(b), each layer 31 is formed from a parallel
arrangement of three pultrusion strips 34 of equal width laid
together side by side. In FIG. 6(c), each layer 31 has either three
or four pultrusion strips 34 in a parallel side-by-side
arrangement, but containing pultrusion strips 34 of two different
widths.
[0138] In the preferred embodiments, each of the pultrusion strips
34 within the above three arrangements extends the full length of
the respective layer 31, although it may be beneficial in some
embodiments for at least some of the layers 31 to include shorter
strips 34 which are arranged end to end.
[0139] FIGS. 7(a) and 7(b) illustrate in greater detail the central
section and root section 12 respectively of the wind turbine blade
showing the X-shaped resilient web 25. The reinforcing structures
are not shown in the drawings, for the sake of clarity. The web is
formed in two generally V-shaped halves 25a, 25b, and the lower
ends of each half 25a, 25b as viewed in the drawings is attached to
the lower half of the outer shell by means of a layer of adhesive
(not shown), and the two halves 25a, 25b of the web 25 are joined
together by bolts 36.
[0140] FIG. 8 is a longitudinal cross-sectional view illustrating
in greater detail the region of the outer shell which includes a
reinforcing structure 22 within a lower half-mould 37. During
manufacture, the outer skin 19, in the form of a dry fibre cloth,
or a plurality of superposed and/or overlapping dry fibre cloths,
is first placed on the surface of the half-mould 37, and elongate
wedges 29 are then positioned on the outer skin 19 along the
curvilinear regions where the reinforcing structures 9, 10, 11, 22,
23, 24 are to be positioned. The inner skin, described further
below, is also formed by a dry fibre cloth, or a plurality of
superposed and/or overlapping dry fibre cloths. The dry cloths are,
once positioned in the half-moulds with other components as
described below, impregnated with resin supplied into the
half-moulds, e.g. in an infusion process, such as the one described
below. It should be pointed out that as an alternative, also
mentioned below, the inner and outer skin could be provided from
prepreg (pre-impregnated fibre) cloths, where the resin is supplied
into the half-moulds together with the fibre material of the
cloths.
[0141] The reinforcing structures are positioned along respective
upper surfaces of the wedges 29. This can be achieved by firstly
positioning the U-shaped channel 28 of each reinforcing structure
along the upper surface of the wedge 29 and then introducing the
stack 27 of pultruded layers of fibrous composite strips into the
channel 28, or alternatively forming the entire reinforcing
structure outside the half-mould 37 and then placing it along the
upper surface of the wedge 29. In either case, the reinforcing
structure can be lowered into position on the wedge 29 or slid into
position along the surface of the wedge 29.
[0142] The orientation of the upper surfaces of the wedges 29 is
varied along their length in dependence on the curvature of the
linear regions so as to retain the reinforcing structures in the
desired positions.
[0143] A layer of structural foam 17 is then introduced into the
half-mould 37 to fill the regions between the reinforcing
structures 9, 10, 11, 22, 23, 24. The inner skin 18, in the form of
a dry fibre cloth, or a plurality of superposed and/or overlapping
dry fibre cloths, is then placed on the upper surfaces of the
reinforcing structures and the structural foam 17 and the
components covered with an airtight bag to form an evacuation
chamber which is subsequently evacuated and resin introduced, as
described in greater detail below.
[0144] The components within the lower half-mould 37 are then
heated and the resin thereby cured so as to form the lower outer
half-shell of the blade.
[0145] The inner skin 18 and the outer skin 19 are formed in this
embodiment from a layer of biax glass cloth, although multiple
layers may alternatively be used. As mentioned above, it would also
be possible to omit the U-shaped channel 28 and the elongate wedges
29 so that the stack 27 is formed and located directly on the outer
skin 19. It would also be possible to position the structural foam
17 on the outer skin 19 and then subsequently to introduce the
stack 28 into the mould 37.
[0146] An upper half-mould with an outer shell is then positioned
above the lower half-mould 37 mould so as to form the complete
outer shell of the blade.
[0147] FIG. 9(a) illustrates the overall structure of the
components of the lower half of the outer shell when in the lower
mould-half 37. Referring to FIG. 9(b), after the inner skin 18 has
been placed over the surface of the reinforcing structures 22, 23
and the upper surface of the structural foam 17, an air-tight
sealing layer (i.e. a vacuum bag) 38 is attached to the mould so as
form an evacuation chamber encapsulating all of the components, and
the chamber is then evacuated using a vacuum pump 39. With the pump
39 still energised, a supply of liquid resin 40 is connected to the
chamber so as to infuse both the components and the interstitial
spaces therebetween. A corresponding infusion process is applied to
the components of the upper half of the outer shell. The pump 39
continues to operate during a subsequent moulding operation in
which the mould is heated so as to cure the resin, although during
the curing process the extent of de-pressurisation may be
lowered.
[0148] The X-shaped web 25 and the Z-shaped web 26 are then
attached by means of adhesive to the inner skin 18 immediately
above the reinforcing structures 22, 23, 24 in the lower half-mould
37, and the upper free ends of the webs 25, 26 are coated with
respective layers of adhesive.
[0149] The upper half-mould is then pivoted into position above the
lower half-mould 37, and the two half-moulds connected together.
This causes the reinforcing structures 9, 10, 11 within the upper
half-mould to adhere to the upper free ends of the webs 25, 26. The
resilient nature of the webs 25, 26 give rise to a biasing force of
the webs 25, 26 against the upper reinforcing structures 9, 10, 11
so as to ensure good adhesion. The leading edge of the blade is
formed along leading edges of the respective half-moulds, and
trailing edge of the blade is formed along trailing edges of the
respective half-moulds.
[0150] The mould is then opened, and the finished turbine blade
lifted from the mould.
[0151] FIGS. 10(a) to 10(f) are cross-sectional illustrations of
alternative embodiments of wind turbine blades in which each of the
webs 41, 42, 43 is of I-shaped cross section, which, in combination
with the associated reinforcing structures, results in an I-beam
construction. Since each of the webs is provided with a flange 30
at each end, these could alternatively be considered as C-section
webs, where the arms of the C-shape constitute the flanges 30.
[0152] In FIGS. 10(a) to 10(c), there are only four reinforcing
structures 9, 10, 22, 23. FIG. 10(a) represents a cross sectional
view near the blade tip, FIG. 10(b) a sectional view mid-way along
the blade, and FIG. 10(c) a sectional view near the root end, where
it can be seen that the thickness of the reinforcing structure 9,
10, 22, 23 is tapered. As can be seen from the drawings, the
reinforcing structures within each half-shell are closer together
near the tip of the blade.
[0153] In FIGS. 10(d) to 10(f), there are six reinforcing
structures 9, 10, 11, 22, 23, 24, and a respective I-shaped web 41,
42, 43 linking each pair of opposed structures 9, 19; 10, 23; and
11, 24. FIG. 10(d) represents a cross sectional view near the blade
tip, FIG. 10(e) a sectional view mid-way along the blade, and FIG.
10(f) a sectional view near the root end, where again it can be
seen that the thickness of the reinforcing structure 9, 10, 22, 23
is tapered.
[0154] FIGS. 11(a) and 11(b) illustrate two further forms of web.
In FIG. 11(a), the web 44 has an X-shaped cross section in which
the two diagonals are bent at the intersection 45, so that the
upper limbs diverge at an angle .alpha. which is greater than the
angle .beta. between the lower two limbs. An advantage of this
arrangement is that the upper wide angle gives rise to additional
flexibility when the two half-moulds are closed, while the lower
limbs serve merely to bridge the gap between the two shells. In
FIG. 11(b), the lower two limbs have been combined into a single
limb, resulting in a web 46 of Y-shaped cross section. Such a web
can replace the X-shaped and/or Z-shaped webs described above.
[0155] Referring to FIG. 12, the method described above can be
summarised as comprising a step 47 of providing the support surface
within the lower half-mould 37, a step 48 of introducing
reinforcing structures 9 into the lower half-mould 37 and a step 49
of sliding the reinforcing structures 9 along the surface of the
wedge 29 into the respective desired positions.
[0156] FIG. 13 illustrates an alternative method, in which the
pultruded strips 34 are placed in a separate mould, provided as a
U-shaped channel 28, outside of the main half-mould 50, together
with a matrix (resin or adhesive) which is pre-cured so that the
stack 27 is formed in the separate mould 28. The pre-cured cured
stack 27 is then placed in the main half-mould 50 for an infusion
resin process together with the other structural elements.
[0157] Referring to FIG. 14, this method can be summarised as
comprising the following steps: (a) forming a stack of fibrous
layers 51; (b) pre-curing the stack of fibrous layers in a first
mould 52; (c) introducing the pre-cured stack into a second mould
53; and (d) integrating the stack and the other structural elements
together in the second mould 54.
[0158] In some embodiments, the stack can be partially cured in the
first mould and then fully cured in the second mould. In other
embodiments the stack can be fully cured in the first mould and
integrated as such with the other structural elements in the second
mould wherein some of other structural elements are cured.
[0159] FIGS. 15(a) to 15(c) illustrate schematically a further
preferred embodiment, which may be combined with any of the
embodiments described above. For the sake of enhanced clarity, the
elements are not drawn to scale. In each half-shell 8 there are
provided inner and outer pre-cured meshes 55, 56 formed from glass
weave and pre-cured resin, and these are positioned between the
respective inner and outer skins 18, 19 and the underlying
reinforcing structures 9, 10. The meshes 55, 56 extend over the
regions where the underlying reinforcing structures 9, 10 abut the
core material 17. In the region of the blade tip 13, the two
reinforcing structures 9, 10 are closely separated, as illustrated
in the cross-sectional view of FIG. 15(a) taken along the line A-A'
of FIG. 15(c). In this case, each of the inner and outer meshes 55,
56 extends across both of the underlying reinforcing structures 9,
10, so as to cover all of the four transition regions between the
reinforcing structure 9, 10 and the core material 17. However, in
the region of the root section 12 of the blade, the two reinforcing
structures 9, 10 are further apart, as illustrated in the
cross-sectional view of FIG. 15(b) taken along the line B-B' of
FIG. 15(c). In this case, each of the inner and outer meshes 55, 56
extends across only a respective one of the underlying reinforcing
structures 9, 10, so as to cover only the two transition regions
between the respective reinforcing structure, e.g. 9 and the
adjacent core material 17.
[0160] The function of the inner and outer meshes 55, 56 is to
prevent the inner and outer skins 17, 18 from wrinkling due to: (a)
gaps between the underlying reinforcing structures 9, 10 and the
adjacent core material 17; and (b) any slight differences between
the thickness of the underlying reinforcing structures 9, 10 and
the thickness of the core material 17.
[0161] FIG. 15(c) is a plan view of this arrangement, from which it
can be seen that the meshes 55, 56 form an approximate V-shape. The
outlines of the reinforcing structures 9, 10 sandwiched between the
inner and outer meshes 55, 56 are illustrated in the drawing by the
dashed line. The side edges of the inner and outer meshes 55, 56
extend about 20 mm over the underlying core material. It would also
be possible to provide a single pre-cured mesh 55 located under the
reinforcing structures 9, 10 and the core material 17. However, in
practice, it is beneficial for the layup, i.e. the inner and outer
layers 17, 18, the reinforcing structures 9,10 and the foam 17, to
be symmetrical about a mid-point plane of the layup.
[0162] It will be appreciated that numerous variations to the above
embodiments may be made without departing from the scope of the
present invention which is defined solely by the following claims.
For example, although in the preferred embodiment there are six
reinforcing structures and both an X-shaped web and a Z-shaped web,
alternative embodiments may comprise only four reinforcing
structures and a single X-shaped web.
[0163] In a further example, as opposed to using the resin infusion
method of manufacturing the blade described above with reference to
FIG. 9(b), fibres which are pre-impregnated with resin (i.e.
"pre-preg" fibres) may be used for the inner and outer skins, in
which case it would not be necessary to infuse resin into the shell
construction. In this arrangement, adhesive film layers can be
provided between the individual layers in the stack so that they
adhere together when the structure is cured.
* * * * *